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Xenon strobe

Discussion in 'Electronic Design' started by Mike, Dec 28, 2007.

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  1. Mike

    Mike Guest

    Hi

    Does anyone know how to build a xenon strobe so that it has a very tight
    flash to flash repeatability.
    I have a circuit with which the frequency is only 1 flash per second at
    about 0.35 Joules (6.6uf and 325v), but I am getting a significant (12%)
    flash to flash brightness change. The supply voltage (325v) is from a DC DC
    converter and is very stable.

    Any comments would be greatly appreciated.

    Thanks
    Mike
     
  2. Glen Walpert

    Glen Walpert Guest

    Is that 12% variation in total light output integrated over the
    duration, or peak?

    I did not look at light output when testing my flash, but I did find
    that both peak current and delay between trigger and flash varied
    quite a bit when I had a just adequate trigger voltage. With just
    enough trigger to reliably flash I had random delays from 3 to 20
    usec, and about 10% variation in peak current. With the maximum
    trigger voltage I had available (20 kV) the timing jitter went down to
    around 1 usec and the peak current variability reduced to a few
    percent, less after the tube warmed up a bit, which only took about 10
    shots at 5/sec and 18 J. So you could try a higher voltage trigger
    transformer and see if that helps, or try your existing trigger
    transformer from a separate supply at its highest allowable primary
    voltage.

    The peak current of my flash also increased around 5% as the tube
    warmed up. So the best way to get uniform total light output despite
    thermal (and other) effects might be to integrate light output as
    measured by your PIN diode and shut the flash tube current off when
    you have enough.

    Glen
     
  3. Mike

    Mike Guest

    The 12% change that I am seeing is in the integrated light output, using a
    photodiode and integrator circuit.
    In practice, the strobe is used with a camera and the exposure of each shot
    is also visibly different.
    I have built a "rough" circuit with a IGBT to turn off the lamp when the
    integrated potodiode signal reaches a threshold. The circuit works and I am
    able to control the overall brightness of the flash now but still get up to
    12% flash to flash difference. I believe that this is due to the delays in
    the photodiode / integrator etc, such that the feedback signal are out of
    phase with the actual light output from the lamp, and the variation is not
    being removed. I think that this does suggest that the variation is in the
    brightness of the initial burn of the lamp. I need to make a faster feedbak
    circuit to get better results.

    I will also take your advice (Glen) and try increasinging the trigger
    voltage.
     
  4. Glen Walpert

    Glen Walpert Guest

    The faster feedback sounds like a good idea to me. The IGBT gate
    drive might be the hardest part to make fast, you will need a driver
    that can sink a lot of current to get the gate charge out fast.

    Also make sure your PIN diode is not saturating and missing variations
    in peak brightness, if it is monitoring the flashtube directly instead
    of reflected scene light this could be a problem.
     
  5. Mike

    Mike Guest


    Thanks for the advice

    Mike
     
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